error assertion failed with Intel C++ Compiler 17.0

Hello,

I had this compilation error with Intel C++ Compiler 17.0 and Visual Studio 2015.

1>C:\libressl-2.5.0\tls\tls_util.c(157): error : assertion failed: construct_message: not all fill-ins used (shared/cfe/edgcpfe/error.c, line 3586)
1>
1>      return (buf);

Source code is like this,

uint8_t *
tls_load_file(const char *name, size_t *len, char *password)
{
...
	char *data, *buf = NULL;
...
	return (buf);

This function is defined as returning (uint8_t *), but it returns (char *).

If I cast 'buf' by (uint8_t *), compilation error is resolved.
I think this could be a warning, though, should not be treated as an error.

Is this a compiler bug, or not ?

source code is here.
https://github.com/libressl-portable/openbsd/blob/master/src/lib/libtls/tls_util.c

and related report is here.
https://github.com/libressl-portable/portable/issues/209#issuecomment-249587024

Best regards,